1. Field of the invention
The present invention relates to a method and apparatus for burning liquid fuel in a wide range of applications from household oil stoves up to industrial furnaces.
2. Description of the prior art
Liquid fuel is burned for space heating (in stoves, for example), for heating materials, for powering prime movers such as internal combustion engines, and for other such purposes.
A heretofore known practice is to burn liquid fuel which is either directly gasified or which is finely vaporized by an atomizer.
The former method of burning the directly gasified fuel is widely used in general household oil stoves, typical of which are a pot type (JU-A-No. 35713/1983), a wick type (JP-A-No. 203307/1983 and No. 64134/1985) and a vaporization type (JIS 3030).
The pot type employs a burner bowl in which fuel is vaporized before being burned and is equipped with a combination of vaporization and combustion units. The wick type has a wick of asbestos or the like which is partially inserted into a fuel tank so as to absorb fuel from the tank. The wick is formed to have a large surface area so as to facilitate evaporation of the fuel. When the fuel absorbed by the wick is ignited, the flame spreads over the entire exposed area of the wick and continuous combustion ensues.
In the case of the vaporization type, fuel is vaporized in a vaporization chamber or pipe and then burned in a combustion unit, the vaporization unit being separated from the combustion unit.
Although the method of burning gasified fuel is used in some household oil stoves, it is more widely used in industrial furnaces, boilers and the like. This burning method is designed to promote vaporization and combustion reaction by gasifying liquid fuel into fine oil drops to increase the contact area of each drop with air.
Oil burners generally in use are adapted to burn fuel by means of a rotary burner, jet burner (vaporization spray, air spray and mechanical spray), special burner (gun-type high-pressure spray and low pressure spray) or the like. There are also examples having a kind of ignition device for igniting liquid fuel in the form of foam (JP-B-No. 42018/1974, JP-A-No. 38368/1972).
In the method of burning liquid fuel which is directly gasified using a pot, it is difficult to quickly increase combustion until the combustion chamber is sufficiently warmed after the fuel is ignited. Consequently, it takes a fairly long time before such oil stoves radiate heat satisfactorily after the fuel is ignited. In the case of the wick-type burning method, the range over which combustion can be adjusted is small and, depending on atmospheric conditions and the room size, it may be impossible to obtain ideal heating.
Moreover, there is generated an offensive smell from oil stoves when fuel is ignited or the flame is extinguished and this has caused oil stoves to be known for their bad odor.
From the point of safety, the flame in an oil stove has to be extinguishable as quickly as possible (e.g., according to JIS, the flame in the oil stove has to be extinguished within 10 seconds after an earthquake occurs or when it is tipped over by accident). The offensive smell generated when it is turned off therefore tends to become stronger.
This means the flame of an oil stove is required to be extinguished as quickly as possible after flame extinguishment is initiated. In the case of an oil stove, for instance, fuel is prevented from being vaporized from the wick or pot after the flame is extinguished and it is oxidized into aldehydes producing an irritant smell while passing through the hot combustion chamber. The problem is that the resulting strong offensive smell gives users an uncomfortable feeling.
Although there are many kinds of combustion equipment using the spray combustion method, they all allow groups of oil drops to have a wide distribution of particle sizes when they are dispersed by air; and these drops act on one another and move in different directions at different speeds.
As a result, spray combustion lacks uniformity, because oil drops insufficiently vaporized and mixed reach the front face of the flame before being enclosed in diffusion flame. The flame tends to become nonuniform, causing partial overheating of parts being heated.
Moreover, a device for spraying the oil is required and this results in high running costs such as high power cost.
In addition to the aforementioned disadvantages, the devices proposed in JP-B-No. 42018/1974 and JP-A-No. 38368/1972 function as ignition devices and are incapable of promoting continuous stable combustion.